I. Field of the Invention
The present invention relates generally to the fields of microbiology, and clinical bacteriology. More particularly, it concerns sequences of the uspA1 and uspA2 genes which encode the proteins UspA1 and UspA2, respectively, both of which encode an epitope reactive with monoclonal antibody (MAb) 17C7 and provide useful epitopes for immunodiagnosis and immunoprophylaxis.
II. Description of Related Art
It was previously thought that Moraxella catarrhalis, previously known as Branhamella catarrhalis or Neisseria catarrhalis, was a harmless saprophyte of the upper respiratory tract (Catlin, 1990; Berk, 1990). However, during the previous decade, it has been determined that this organism is an important human pathogen. Indeed, it has been established that this Gram-negative diplococcus is the cause of a number of human infections (Murphy, 1989). M. catarrhalis is now known to be the third most common cause of both acute and chronic otitis media (Catlin, 1990; Faden et al., 1990; 1991; Marchant, 1990), the most common disease for which infants and children receive health care according to the 1989 Consensus Report. This organism also causes acute maxillary sinusitis, generalized infections of the lower respiratory tract (Murphy and Loeb, 1989) and is an important cause of bronchopulmonary infections in patients with underlying chronic lung disease and, less frequently, of systemic infections in immunocompromised patients (Melendez and Johnson, 1990; Sarubbi et al., 1990; Schonheyder and Ejlertsen, 1989; Wright and Wallace, 1989).
The 1989 Consensus Report further concluded that prevention of otitis media is an important health care goal due to both its occurrence in infants and children, as well as certain populations of all age groups. In fact, the total financial burden of otitis media has been estimated to be at least $2.5 billion annually. Vaccines were identified as the most desired approach to prevent this disease for a number of reasons. For example, it was estimated that if vaccines could reduce the incidence of otitis media by 30%, then the annual health care savings would be at least $400 million. However, while some progress has been made in the development of vaccines for 2 of the 3 common otitis media pathogens, Streptococcus pneumoniae and Haemophilus influenzae, there is no indication that similar progress has been made with respect to M. catarrhalis. This is particularly troublesome in that M. catarrhalis now accounts for approximately 17-20% of all otitis media infection (Murphy, 1989). In addition, M. catarrhalis is also a significant cause of sinusitis (van Cauwenberge et al., 1993) and persistent cough (Gottfarb and Brauner, 1994) in children. In the elderly, it infects patients with predisposing conditions such as chronic obstructive pulmonary disease (COPD) and other chronic cardiopulmonary conditions (Boyle et al., 1991; Davies and Maesen, 1988; Hager et al., 1987).
Despite its recognized virulence potential, little is known about the mechanisms employed by M. catarrhalis in the production of disease or about host factors governing immunity to this pathogen. An antibody response to M. catarrhalis otitis media has been documented by means of an ELISA system using whole M. catarrhalis cells as antigen and acute and convalescent sera or middle ear fluid as the source of antibody (Leinonen et al., 1981). The development of serum bactericidal antibody during M. catarrhalis infection in adults was shown to be dependent on the classical complement pathway (Chapman et al., 1985). And more recently, it was reported that young children with M. catarrhalis otitis media develop an antibody response in the middle ear but fail to develop a systemic antibody response in a uniform manner (Faden et al., 1992).
Previous attempts have been made to identify and characterize M. catarrhalis antigens that would serve as potentially important targets of the human immune response to infection (Murphy, 1989; Goldblatt et al., 1990; Murphy et al, 1990). Generally speaking, the surface of M. catarrhalis is composed of outer membrane proteins (OMPs), lipooligosaccharide (LOS) and fimbriae. M. catarrhalis appears to be somewhat distinct from other Gram-negative bacteria in that attempts to isolate the outer membrane of this organism using detergent fractionation of cell envelopes has generally proven to be unsuccessful in that the procedures did not yield consistent results (Murphy, 1989; Murphy and Loeb, 1989). Moreover, preparations were found to be contaminated with cytoplasmic membranes, suggesting an unusual characteristic of the M. catarrhalis cell envelope.
Passive immunization with polyclonal antisera raised against outer membrane vesicles of the M. catarrhalis strain O35E was also found to protect against pulmonary challenge by the heterologous M. catarrhalis strain TTA24. In addition, active immunization with M. catarrhalis outer membrane vesicles resulted in enhanced clearance of this organism from the lungs after challenge. The positive effect of immunization in pulmonary clearance indicates that antibodies play a major role in immunoprotection from this pathogen. In addition, the protection observed against pulmonary challenge with a heterologous M. catarrhalis strain demonstrates that one or more conserved surface antigens are targets for antibodies which function to enhance clearance of M. catarrhalis from the lungs.
Outer membrane proteins (OMPs) constitute major antigenic determinants of this unencapsulated organism (Bartos and Murphy, 1988) and different strains share remarkably similar OMP profiles (Bartos and Murphy, 1988; Murphy and Bartos, 1989). At least thee different surface-exposed outer membrane antigens have been shown to be well-conserved among M. catarrhalis strains; these include the 81 kDa CopB OMP (Helminen et al., 1993b), the heat-modifiable CD OMP (Murphy et al., 1993) and the high-molecular weight UspA antigen (Helminen et al., 1994). Of these three antigens, both the CopB protein and UspA antigen have been shown to bind antibodies which exert biological activity against M. catarrhalis in an animal model (Helminen al., 1994; Murphy et al., 1993).
The MAb, designated 17C7, was described as binding to UspA, a very high molecular weight protein that migrated with an apparent molecular weight (in SDS-PAGE) of at least 250 kDa (Helminen et al., 1994; Klingman and Murphy, 1994). MAb 17C7 enhanced pulmonary clearance of M. catarrhalis from the lungs of mice when used in passive immunization studies and, in colony blot radioimmunoassay analysis, bound to every isolate of M. catarrhalis examined. This same MAb also reacted, although less intensely, with another antigen band of approximately 100 kDa, as described in U.S. Pat. No. 5,552,146 (incorporated herein by reference). A recombinant bacteriophage that contained a fragment of M. catarrhalis chromosomal DNA that expressed a protein product that bound MAb 17C7 was also identified and migrated at a rate similar or indistinguishable from that of the native UspA antigen from M. catarrhalis (Helminen et al., 1994).
With the rising importance of this pathogen in respiratory tract infections, identification of the surface components of this bacterium involved in virulence expression and immunity is becoming more important. To date, there are no vaccines available, against any other OMP, LOS or fimbriae, that induce protective antibodies against M. catarrhalis. Thus, it is clear that there remains a need to identify and characterize useful antigens and which can be employed in the preparation of immunoprophylactic reagents. Additionally, once such an antigen or antigens is identified, there is a need for providing methods and compositions which will allow the preparation of vaccines and in quantities that will allow their use on a wide scale basis in prophylactic protocols.
It is, therefore, an object of the present invention to provide new UspA1 and UspA2 proteins and genes coding therefor. It also is an object of the present invention to provide methods of using these new proteins, for example, in the preparation of agents for the treatment and inhibition of M. catarrhalis infection. It also is contemplated that through the use of other technologies such as antibody treatment and immunoprophylaxis that one can inhibit or even prevent M. catarrhalis infections.
In satisfying these goals, there are provided epitopic core sequences of UspA1 and UspA2 which can serve as the basis for the preparation of therapeutic or prophylactic compositions or vaccines which comprise peptides of 7, 10, 20, 30, 40, 50 or even 60 amino acids in length that elicit an antigenic reaction and a pharmaceutically acceptable buffer or diluent. These peptides may be coupled to a carrier, adjuvant, another peptide or other molecule such that an effective antigenic response to M. catarrhalis is retained or even enhanced. Alternatively, these peptides may act as carriers themselves when coupled to another peptide or other molecule that elicits an antigenic response to M. catarrhalis or another pathogen. For example, UspA2 can serve as a carrier for an oligosaccharide.
In one embodiment, the epitopic core sequences of UspA1 and UspA2 comprise one or more isolated peptides of 7, 10, 20, 30, 40, 50 or even 60 amino acids in length having the amino acid sequence AQQQDQH (SEQ ID NO:17).
In another embodiment, there are provided nucleic acids, uspA1 and uspA2, which encode the UspA1 and the UspA2 antigens, respectively, as well as the amino acid sequences of the UspA1 and UspA2 antigens of the M. catarrhalis isolates O35E, TTA24, TTA37, and O46E. It is envisioned that nucleic acid segments and fragments of the genes uspA1 and uspA2 and the UspA1 and UspA2 antigens will be of value in the preparation and use of therapeutic or prophylactic compositions or vaccines for treating, inhibiting or even preventing M. catarrhalis infections.
In another embodiment, there is provided a method for inducing an immune response in a mammal comprising the step of providing to the mammal an antigenic composition that comprises an isolated peptide of about 20 to about 60 amino acids that contains the identified epitopic core sequence and a pharmaceutically acceptable buffer or diluent.
In another embodiment, there is provided a method for diagnosing M. catarrhalis infection which comprises the step of determining the presence, in a sample, of an M. catarrhalis amino acid sequence corresponding to residues of the epitopic core sequences of either the UspA1 or UspA2 antigen. This method may comprise PCR(trademark) detection of the nucleotide sequences or alternatively an immunologic reactivity of an antibody to either a UspA1 or UspA2 antigen.
In a further embodiment, there is provided a method for treating an individual having an M. catarrhalis infection which comprises providing to the individual an isolated peptide of about 20 to about 60 amino acids that comprises at least about 10 consecutive residues of the amino acid sequence identified as an epitopic core sequence of UspA1 or UspA2.
In a still further embodiment, there is provided a method for preventing or limiting an M. catarrhalis infection that comprises providing to a subject an antibody that reacts immunologically with the identified epitopic core region of either UspA1 or UspA2 of M. catarrhalis. 
In another embodiment, there is provided a method for screening a peptide for reactivity with an antibody that binds immunologically to UspA1, UspA2 or both which comprises the steps of providing the peptide and contacting the peptide with the antibody and then determining the binding of the antibody to the peptide. This method may comprise an immunoassay such as a western blot, an ELISA, an RIA or an immunoaffinity separation.
In a still further embodiment, there is provided a method for screening a UspA1 or UspA2 peptide for its ability to induce a protective immune response against M. catarrhalis by providing the peptide, administering it in a suitable form to an experimental animal, challenging the animal with M. catarrhalis and then assaying for an M. catarrhalis infection in the animal. It is envisioned that the animal used will be a mouse that is challenged by a pulmonary exposure to M. catarrhalis and that the assaying comprises assessing the degree of pulmonary clearance by the mouse.
Other objects, features and advantages of the present invention will become apparent from the following detailed description It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within tie spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.